Prior to the present invention a variety of surfactants are disclosed in the literature which are indicated to be suitable for use in mechanical dishwasher formulations. Many of the surfactants disclosed are block polyalkylene oxide copolymers of long chain alkyl started alkoxylates. For example, U.S. Pat. No. 2,677,700 which issued May 4, 1954 and is assigned to Wyandotte Chemicals Corporation discloses and claims certain polymers anionic and nonionic surface active agents in which the essential hydrophobic element is a polyoxyalkylene chain of a prescribed minimum length. It is indicated in the patent that both the hydrophobic and hydrophilic elements can be simultaneously varied both as to the molecular weight and type to prepare a "tailored" surface active agent.
In U.S. Pat. No. 2,674,619 which issued Apr. 6, 1954 and is also assigned to Wyandotte Chemicals Corporation there is disclosed a new class of polyalkyleneoxy compositions which are indicated to have outstanding detergent and surface active properties. Such polyalkyleneoxy compositions are prepared by first condensing propylene oxide with an organic compound having a plurality of reactive hydrogen atoms to prepare a polyoxypropylene polymer of at least 900 molecular weight, and subsequently condensing ethylene oxide therewith.
There is also disclosed in U.S. Pat. No. 4,134,854 which issued to Texaco Development Corporation on Jan. 16, 1979, surfactants wherein the pour point can be lowered by the addition of alkylene oxides. In the process disclosed in this patent, ethylene oxide, propylene oxide and ethylene oxide are added sequentially to alcohols.
Other surfactants are disclosed in the literature which have been indicated to be useful in dishwasher formulations and which have various desirable properties, such as low cloud points, excellenet defoaming characteristics and the like. However, for the most part these references are directed to surfactants which are either prepared from block copolymers as opposed to random copolymers or which rely upon the addition of a second or third component to make up for the deficiencies of the surfactant.
In this regard, see for example, U.S. Pat. No. 3,629,127 which discloses and claims the use of nonionic surfactants such as oxyalkylated linear alcohols in addition to an auxiliary defoamant, for example, an anionic phosphate ester of oxyalkylated alcohols. In a similar fashion, in U.S. Pat. No. 3,635,827 low foam dishwasher detergent surfactants are prepared by utilizing alkoxylates of fatty alcohols in combination with polyvinyl alcohol. In U.S. Pat. Nos. 3,941,710, 4,001,132, and 4,203,858, there are disclosed various combinations of polymeric compounds and additives to achieve desired properties in the surfactants disclosed and claimed.
U.S. Pat. No. 3,359,207 which was issued Dec. 19, 1967, describes the use of block copolymers of ethylene and propylene oxide and block copolymers derived from various starters such as pentaerythritol, ethanol, ethylene diamine, octanol and the like. Similar ethylene oxide/propylene oxide block copolymers, which use branched 1-decanols as starters are also described in U.S. Pat. No. 4,299,994. Other patents such as U.S. Pat. Nos. 3,101,374, 4,306,987 and 4,411,810 disclose various block-heteric copolymers which are useful as surfactants.
Additives for automatic dishwasher detergent formulations comprising PO/EO/PO block copolymers in combination with an alkyl phosphate ester are also described in U.S. Pat. Nos. 4,070,298 and 4,263,160. It is indicated that such additives are useful in automatic dishwasher formulations to accomplish defoaming.
U.S. Pat. No. 4,272,394 describes blends of low foaming nonionic surfactants which are replacements for the alkyl phosphate ester defoamants of conventional automatic dishwashing detergents. Such blends comprise a conventional low foaming nonionic surfactant and a block-heteric copolymer of ethylene oxide and a lower alkylene oxide such as propylene or butylene oxide. The conventiona low foaming nonionic surfactant is a polyoxyalkylene adduct of a hydrophobic base wherein the oxygen/carbon atom ratio in the oxyalkylene portion of the molecule is greater than 0.40, and is prepared from, e.g., ethylene oxide or mixtures with minor amounts of propylene oxide, butylene oxide, etc. In this regard, see, e.g., column 2, lines 45+, as well as column 6, lines 64+.
As can be seen from the foregoing, the literature relating to the use of ethylene oxide/propylene oxide copolymers as surfactants for mechanical dishwasher detergents discloses, for the most part, nonionic surfactants which contain three possible configurations. First, the ethylene oxide/propylene oxide is a block configuration, that is, either EO/PO/EO or PO/EO/PO. Second, the ethylene and propylene oxide are reacted with alcohol starters having eight or more carbon atoms. Finally, heteric copolymers containing ethylene or propylene oxide can be used if in a block heteric form. Copolymers, such as these are formed by preparing a random copolymer with two regions where the EO/PO random mixture is adjusted to prepare a relatively hydrophilic and a relatively hydrophobic region.